I get the same error message. I get it at system start up and reboot, and have to click twice to get rid of it.

I have been doing some reading and in one post it suggested that windows is scanning for drives that it can't find.

I recently (September) reinstalled my operating system (XP Pro SP2) from scratch but did not format the rest of the HD. I have several partitions - 2 primary (NTFS and EXT 3) and 3 logical(1 - FAT32, 2 - NTFS), as well as an external USB HD (FAT32).

Windows assigned new drive letters to all the drives. I have not changed any of these. Is it possible that windows is 'remembering' old drive pathways from the various drive master boot records and is complaining because they don't match with my current system set up?

I had this very same error message after installing acronis true image 11 and disk director on XP Pro. I followed the advice given to clear the task bar list and the problem went away. Talk about an obscure problem. I am really glad I found this thread.